I have played this game on and off in the past year or so and here are some things I have to say about it.
Gameplay: I love how simple yet detailed this game especially with combat which is the focus of the game. When you fight the enemy there is a bar that pops up on the bottom of the screen that determines what your character does depending on where a line lands. That line is controlled by you, so that if you are good at timing things then this game rewards you with a damage multiplier. That's not including the beautiful mercenaries that assist you from the side. With their abilities that range from healing, burning, or just dealing flat damage.
Also gear is a major part of the game since it's the main/only way you increase your stats. Which brings us to upgrading. There are multiple types of upgrading that you can such as leveling up equipment, upping their rarity, or calibrating. Upgrading increases the basic stats which includes the perks that the equipment has (perks can be changed to). Upping rarity also increases the basic stats of the equipment along with adding more perks to it. And calibrating your equipment increases everything by a certain percentage every time you calibrate it.
The main way you can acquire gear is through fighting strongholds that are filled with enemies, loot chests, random events, and a boss at the end which is stronger than any enemies on that level. And if you don't want to constantly be online all the time be sure to do your afk tasks. So you can get extra items and increasing your base stats at the same time, all while you are gone and on your way.
Over all this game is pretty solid in my opinion and is pretty decent for a mobile game.